While he was at Harvard, his passion for ornithology flourished; he birded with noted ornithologists Ludlow Griscom, William H. Drury, Wendell Taber, Allan Cruickshank, Chandler Robbins, Charles Foster Batchelder and others in the Nuttall Ornithological Club.

They were married in 1943 and had five children, and he lived in West Hartford, Connecticut, for the rest of his life.

Bergstrom's volunteer leadership roles in ornithology had a range of impacts from local to international.

From 1956 until his death in 1973, he imported and sold mist nets to bird banders from around the world for NEBBA, and served as their Assistant Treasurer, with the proceeds from the net sales supporting their publications.

[3][4] He was instrumental in getting West Hartford to purchase and develop the Spicebush Swamp as a nature preserve,[5] and also helped the Hartford Audubon Society obtain its 90-acre (360,000 m2) Lewis Farm Bird Sanctuary in Suffield, CT.[6] Bergstrom died on March 21, 1973.